The invention relates to the manufacture of chemicals which sterilize unpotable water, and which are used as additives to the unpotable water during desalination, and to the product (potable) water; specifically using as raw material the waste products of desalination when potable water is a co-product of such chemicals manufacture.
Unpotable water from surface sources (seawater, agricultural field drainage, rivers, ponds, etc.) is sterilized before it is desalinated because microscopic life forms in it form slimes which impede the functioning of desalination equipment. Chemical sterilants, from an external source, the toxic effect of which is neutralized in some suitable way before being discharged to the environment as waste in brine, are preferred for desalination processes involving temperatures no higher than 120.degree. F. (such as reverse osmosis or freeze crystallization of ice). Customarily, chlorine or dissolved hypochlorite anion, which are chemical derivatives of sodium chloride, are added to desalination feedwater, but the survival rate of some slime-forming microorganisms is sufficiently high to coat surfaces, notably of the permeator membranes where slime reduces water production and decreases the useful service life of permeators.
Seawater and agricultural field drainage water, hereinafter referred to as feedwater, contain bicarbonate anion, a dissolved constituent which must be removed for many reasons (for example, it is corrosive to mild steel in the presence of oxygen), but which concentrates in the less-saline product of reverse osmosis. It may be removed from the desalination product only by an extra step, such as aeration of the permeate containing added acid which is at least equivalent to the bicarbonate.
It would be desirable to provide a process which manufactures chemical derivatives of sodium chloride using as raw materials the brine byproduct from desalination, and which uses these derivatives in part to improve the processes of feedwater sterilization, and of bicarbonate removal.